Heavy duty trucks and boats, as well as other vehicles, often carry air or gas powered horns on the surface of their roof, fender or deck. The horns are typically bolted on the surface and directed forward to deliver a powerful warning to those in danger of colliding with the heavy truck or boat. Typically, these horns have a rear sound unit which connects to a long bell, measuring sometimes in excess of 36 inches (1 meter) long which opens at a flared end. The bell is bolted to the vehicle pointing forward so that its warning blast is best heard by those in front of the vehicle. Because the bell is pointed forwards as the vehicle moves, the bell tends to collect debris including not only snow and rain, but also insects, sand and dirt which have been kicked up into the air in front of the vehicle as it travels. While it is known to put a metal cover over the front of a heavy duty truck air horn, these guards reflect most of the sound coming out of the horn backwards, making it difficult for those in front of the truck to hear the warning blast. It is also known as shown in U.S. Pat. No. 4,171,678, to place a weather shield over the front of a heavy duty truck horn with slots in it to allow sound to project forwards. However, these slots also allow debris to enter the horn.
Conventional air horns also have other problems. First, because of the length of the bells, most air horns are difficult to ship and store, before they are mounted on the vehicle. Second, when the horn is bolted to the surface of the vehicle, it is difficult to remove and repair or replace. For example, bolts must often be loosened from the underside of the surface to which the horn is applied, requiring interior parts to be temporarily removed. Thus, long horns are typically made in two parts with the front bell section welded, soldered or brazed to the rear section. Attaching the two sections is costly.